In a large skillet, cook ground beef and onions until browned. Remove from heat and drain off excess fat.
Cook noodles according to package directions and drain. Combine noodles and beef in a large bowl, and add the remaining ingredients (except bread crumbs and butter).
Pour mixture into a large casserole or 9"x13” pan. In a medium sized bowl, mix together bread crumbs and melted butter, then sprinkle on top of casserole to finish.
Bake approximately 20-25 minutes or until bread crumbs are brown and crisp. Serve immediately.